The conventional adjustment of the illumination and the color temperature of light-emitting diode (LED) lights is generally performed based on a simple linear correlation between a duty cycle of Pulse Width Modulation (PWM) and the illumination. However, due to LEDs having different characteristics at different temperatures or using different circuit arrangements, the correlation between the LED's illumination/color temperature and the duty cycle may not be a simple linear correlation, so that using the conventional manner of adjustment makes it difficult to accurately output light source corresponding to illumination. Furthermore, the light source apparatus uses an internal micro-controller to operate the calculation of the pulse modulation, but it is limited by the performance of the internal micro-controller, so that it is difficult to generate an accurate calculation result. If the conventional light source apparatus must perform a more complicated calculation, the reaction of the light source apparatus may decrease.